The present invention relates to a head for the linear dimension checking of a mechanical piece, including a support structure, an arm-set, movable with respect to the support structure, with an arm and a feeler, coupled to the arm, for touching a surface of the mechanical piece to be checked, and a sensor, coupled to the arm and the support structure, for generating signals depending on the position of said arm with respect to said support structure. The invention also relates to a system for the linear dimension checking of a mechanical piece, including a head as the one formerly mentioned and a processing unit. Furthermore, the invention relates to a method for the linear dimension checking of a mechanical piece, by means of a checking system including said head and a processing unit.
Gauging or measuring heads of the known type are described, for example, in International patent application WO-A-98/20297.
In the known heads, the serial number that identifies each head is generally indicated on the casing of the head or on a plate fixed to the casing.
Other information, relating to the specific features of the individual head, is fundamental for determining the type of application that the head is intended for. In the case of heads as those described in the previously referred to International patent application, it is necessary to know, for example, among other things, values relating to the arm-ratio (in other terms the relationship existing between the entity of the feeler displacement and the entity of the consequent displacement of movable elements of the sensor), the force of the thrust spring, the pre-stroke and the retraction. Some of these values may have been set during calibration.
The information relating to these and other values is generally reported on a technical sheet that accompanies the head. Furthermore, this information may also be coded in an alfanumeric sequence and indicated on the plate together with the serial number, for the purpose of matching in an indissoluble and unequivocal way all the information that belongs to the individual head, and for enabling anyone who is involved with the specific application of the head, or has to carry out operations for the technical assistance on the head, to identify in a rapid and safe manner the characteristics of the head. The provision of the alfanumeric sequence (or xe2x80x9ccodexe2x80x9d) and the matching of the code to the serial number of the individual head, if, on the one hand, simplifies some handling aspects, by overcoming problems that the possible loss of the technical sheet or the mismatch of technical sheets among different heads may cause, on the other hand does not allow to modifyxe2x80x94in the course of the lifetime of the headxe2x80x94the characteristics identified by the coded values, unless giving up the possibility of having the correct information recorded on the head, or undertaking particular and complex procedures for modifying the code. With regard to performance, the heads as those described in patent application WO-A-98/20297 guarantee a high standard of measurement repeatability for relatively broad measuring ranges (and that obviously depend on the dimensions and on the structure of the head and on the type of sensor or transducer utilized). Some factors that do not enable to obtain extremely high standards of performancexe2x80x94at times requested in particular applicationsxe2x80x94regard the errors and the limits in the linearity of the transducer output signal, and entity variations, however small they may be, of said signal as a consequence of temperature variations.
An object of the present invention is to provide a gauging head that overcomes the disadvantages of the known heads, in particular insofar as the handling of the information relating to the identification and the usage specifications of the head are concerned.
A head according to the invention achieves this object and provides other advantages. One of these advantages consists in the possibility of retaining and handling in a simple, rapid and safe manner a great amount of information relating to the head, in addition to that regarding the formerly mentioned usage specifications, as, for example, information relating to the technical assistance and/or the repair that the head undergoes in the course of its lifetime. In this way there is no need to manage separate documents, generally in the paper form, that, in the case of the known heads are added to the documents that identify and certify special characteristics of each individual head.
It is another object of the invention to provide a system and a checking method with at least a head that overcome the drawbacks caused by variations in the output signal of the sensor due to linearity errors and/or thermal variation.
These and other objects and advantages are achieved by a system and a checking method according to the invention.